1908.] Manurial Value of Sewage Sludge. 693 



cake is scraped from the press-cloths into trucks and either 

 sold to farmers, buried, or tipped. The cost of the process, 

 excluding interest and sinking fund in respect of the pressing 

 plant, may be put at from 2s. to 5s. per ton of pressed cake 

 produced. 



Speaking generally, properly pressed sludge when in the 

 form of a solid cake does not give rise to serious nuisance from 

 smell, and if exposed to the air in dry weather it soon becomes 

 entirely inoffensive. It has, however, a slight smell of fresh 

 sewage, and if kept moist, e.g., if it is exposed to the air during 

 wet weather, it soon becomes putrid and gives rise to offensive 

 odours. For this reason it should, if possible, be stored under 

 cover, until it can be spread over land or dug into trenches or 

 buried. 



Disposal of the Pressed Cake. — Pressed sludge can usually be 

 disposed of to neighbouring farmers at about 6d. per ton. 

 This, however, depends to a considerable extent upon the 

 district in which the sewage works are situated. In some cases, 

 e.g., at Bury, Ealing (Northern Works), Wolverhampton, and 

 Richmond, where the works are situated in densely populated 

 districts, or are far removed from a railway, or in the case of a 

 large town where the amount of sludge is greater than the neigh- 

 bouring farmers require, the pressed cake has to be given away, 

 or a small fee has to be paid for its removal. The form of the 

 pressed cake also affects its saleability ; e.g., at Burnley, where 

 the Corporation break up the pressed cake immediately after 

 pressing, a ready market is now obtained. 



The composition of the pressed cake varies according to its 

 origin. It naturally contains a good deal of lime. In two 

 samples which were analysed 1 -28 and -89 per cent, of total 

 nitrogen were found after drying. The calculated value as 

 judged by the manurial constituents alone is stated to be 

 6s. or ys. per ton, but the actual market value is insignificant, 

 owing to the relatively high cost of carriage upon a mixture 

 containing of necessity a large proportion of water, grit, and 

 carbonaceous matter. 



Manurial Value of Sewage Sludge. — Opinions in regard to the 

 manurial value of sludge were of so conflicting a character that 

 the Commissioners thought it advisable to institute some 

 accurate experiments with various sewage sludges, and with 



